1. Field of the Invention
This invention relates to an electromagnetic actuator, an optical scanner using an electromagnetic actuator and a method of preparing an electromagnetic actuator.
2. Related Background Art
Conventional actuators prepared by utilizing the micro-machining technology are mostly based on the use of electrostatic force or piezoelectric phenomena. However, thanks to the availability of the micro-machining technology for utilizing magnetic materials in recent years, actuators using electromagnetic force have been developed.
FIG. 1 of the accompanying drawings schematically illustrates a linear actuator that utilizes an electromagnetic force for positioning the head of a hard disk as disclosed in U.S. Pat. No. 5,724,015. Referring to FIG. 1, the actuator comprises a pair of cores 1004a, 1004b rigidly secured to a substrate (not shown) and a pair of coils 1005a, 1005b wound around the respective cores along with a movable member 1003 so supported by springs 1007 as to be movable relative to the cores 1004a, 1004b. The above-described structure is formed on the substrate by means of micromachining technology.
As electric power is supplied to the coil 1005a of the actuator, the movable member 1003 is pulled toward the core 1004a to consequently displace the movable member 1003 to the left in FIG. 1. When, on the other hand, the coil 1005b is electrically energized, the movable member 1003 is displaced to the right in FIG. 1. The force F1 generated in the actuator is expressed by formula (1) below;
F1=0.5 xcexc0N12i12w1t1(d1xe2x88x92x1)xe2x88x922xe2x80x83xe2x80x83(1) 
where xcexc0 is the magnetic permeability of vacuum, N1 is the number of turns of the coils, i1 is the electric current made to flow to the coil 1005a or 1005b, w1 is the width of the magnetic pole, t1 is the thickness of the magnetic pole and d1 is the length of the gap. If the spring constant of the springs 1007 is k1, the displacement x1 of the actuator is expressed by using the relationship of formula (2) below;
F1=k1x1xe2x80x83xe2x80x83(2) 
However, since actuators having a configuration as described above by referring to FIG. 1 show a large leakage of magnetic flux, they are accompanied by the problem of a poor energy efficiency. Additionally, since the number of turns of the coils of such an actuator is limited due to the structure where only the stationary members are provided with coils, the actuator is also accompanied by the problem of a weak generated force.
In view of the above identified technological problems of the prior art, it is therefore the object of the present invention to provide an electromagnetic actuator that can minimize the leakage of magnetic flux and hence the power consumption rate to improve the energy efficiency and remarkably increase the force it can generate, an optical scanner comprising such an electromagnetic actuator and also a method of preparing such an electromagnetic actuator.
According to the invention, the above-described object is achieved by providing an electromagnetic actuator comprising:
a stationary member having a first core section carrying a first coil wound around its periphery;
a movable member magnetically coupled with the stationary member with a gap therebetween and having a second core section carrying a second coil wound around its periphery;
a support member for displaceably supporting the movable member relative to the stationary member; and
an electric current source for displacing the movable member relative to the stationary member by supplying electricity to the first and second coils.
In another aspect of the invention, there is provided an optical scanner comprising an electromagnetic actuator according to the invention and a mirror arranged on the movable member of the electromagnetic actuator.
In another aspect of the invention, there is provided an optical scanner comprising an electromagnetic actuator according to the invention and a lens arranged on the movable member of the electromagnetic actuator.
In still another aspect of the invention, there is also provided a method of preparing an electromagnetic actuator comprising a stationary member having a first core section carrying a first coil wound around its periphery, a movable member magnetically coupled with the stationary member with a gap therebetween and having a second core section carrying a second coil wound around its periphery and a support member for displaceably supporting the movable member relative to said stationary member, the method comprising steps of:
forming the stationary member, the movable member and the support member on a single substrate by means of photolithography and plating; and
removing the substrate from under the movable member so as to make the movable member to be supported by the substrate by way of the support member.